As is known, in arthroplasty operations, performed to treat bone or vertebra pathologies, and in operations for the implanting and stabilisation of bone prostheses, acrylic resins or bone cements are usually used to be introduced in the specific area to be treated.
The materials normally used in this field of surgery consist of a liquid phase, generally monomeric, used as a solvent for the polymerisation of a resin in powder form, to which may be added antibiotic drugs, promoters of growth or the like.
For these operations, the resin must be prepared directly in the operating theatre. Consequently, the two phases are initially enclosed in two separate containers and then mixed immediately before introduction into the bone or vertebra area to be treated.
Considering the critical nature of these types of operations, it is most important that the utmost sterility of the resin and the resin dispensing devices be guaranteed at all stages.
Normally, the liquid is kept inside a plastic bag or a glass phial and then poured into a container in which powder has been previously collected. Subsequently, an operator mixes the two components using a spatula driven manually or mechanically. Finally, the compound thus obtained is introduced into a dispensing syringe and then injected under pressure through a special needle, into the bone cavity of the implant.
Such known solutions have the evident and recognised disadvantage of placing the compound into contact with the outside environment, thereby negatively affecting the sterility of the operation and making the resin a hazardous vehicle of infections for the person undergoing therapy. At the same time, the operator is placed in contact with a highly-reactive and toxic monomeric liquid, the vapours of which can freely spread in the work environment, with high risk of inhalation by the operator.
The preparation and the final composition of the mixture is, furthermore, strongly dependent on the particular skill of the operator, and so the risk exists of obtaining cements that are not perfectly homogeneous or, again, with incorrect proportions between the two phases.
In an attempt to overcome the above disadvantages, various solutions have been placed at disposal whereby one or more of such disadvantages are overcome.
From U.S. Pat. No. 5,435,645, in the name of the same applicant, a device is known for mixing bone cements in which the preparation of the cement is carried out in conditions of sterility and safety for the operator. The liquid is in fact initially placed inside a first chamber and then forced to pass into a second chamber containing the powder. This way a cement is also obtained that has the right proportions between monomer and powder.
A drawback of such solution is however represented by the fact that the mixing of the two phases is done by manually shaking the whole device. This operation thus strongly depends on the skill of the single mixing operator. Being naturally impossible to precisely establish the shaking time and energy required to obtain a uniform component mix, it follows that the compound is not always shaken enough and this does not therefore show the most suitable physical characteristics. The operation is also not at all easy.
From WO-A-0183094 a device is known for mixing a bone cement in which the mixture of liquid and solid is favoured by the sliding of an agitator disc inside the mixing chamber. This way, a uniform compound is produced of correct phase proportions. Nevertheless, an evident disadvantage of such solution is represented by the fact that the liquid phase is initially taken from a container by means of a common syringe and then introduced into the mixing chamber. These phases therefore do not guarantee absolute sterility of the cement besides being inconvenient and dangerous for the operator.